Chicago general manager Phil Emery cast a wide net in his search, meeting with at least 13 candidates. Besides Trestman, he also brought back Seattle Seahawks offensive coordinator Darrell Bevell and the Indianapolis Colts' Bruce Arians for second interviews.
Smith was let go after nine years, ending a run that included a trip to the Super Bowl but also saw Chicago miss the playoffs five of the past six seasons.
The Bears, who have scheduled a news conference for Thursday morning, are turning to the 57-year-old Trestman in part because of his background with quarterbacks.
He worked with Bernie Kosar as an assistant at the University of Miami and again when he was on the Browns' staff in the 1980s. Trestman helped the Raiders reach the Super Bowl at the end of the 2002 season with an offense he geared for Rich Gannon, the league's MVP that year.
In recent years, Trestman has worked as a consultant in the NFL and in the offseason helped develop quarterbacks entering the league including Cutler. His biggest task will be maximizing the man behind center and getting the offense to click.
That's something that never really happened under Smith, who helped build a top defense around stars such as Brian Urlacher and Lance Briggs but never could solve the issues on the other side of the ball. The Bears' offense never ranked higher than 15th under Smith, and the problems in that area along with the postseason misses ultimately led to his dismissal.
The Bears have big holes on the offensive line and at tight end, but the No. 1 task is connecting with Cutler. As gifted as he is, questions remain about his makeup and demeanor.
He has one year left on his contract, and the Bears have to figure out if he can lead them to the top. In Chicago, the deck at times has been stacked against him.
His relationship with former offensive coordinator Ron Turner seemed icy, and he took a beating in Mike Martz's system. The offense sputtered this year with Mike Tice calling the plays, and now Cutler will be working in his fourth system since the Bears acquired him from Denver in 2009.
Beside the issues on the line, Cutler also lacked a go-to receiver his first three years in Chicago, but that changed in a big way before this season. The Bears hired Emery to replace the fired Jerry Angelo as GM after a late collapse last year, and although he was given a mandate to work with Smith for at least a year, he was able to retool the roster.
The biggest move? That was the trade with Miami for Brandon Marshall, Cutler's favorite target in Denver.
Marshall set club records for catches and yards, but the Bears still ranked 28th on offense.
It didn't help that receivers Alshon Jeffery and Earl Bennett missed time with injuries or that running back Matt Forte was banged up and uninvolved at times, whether it was in the running or passing game.
The Bears also have an aging core on defense and a big question at middle linebacker. Urlacher has an expiring contract and missed the last four games with a hamstring injury after being limited by a knee problem, and the eight-time Pro Bowler might have played his final down for Chicago.
Pro Bowl cornerback Charles Tillman, star defensive end Julius Peppers and linebacker Lance Briggs all are in their 30s.
Despite having some aging stars, the Bears' defense ranked fifth overall and picked off a league-leading 24 passes while returning an NFL-best eight interceptions for touchdowns.
Their special teams remain a strong point, too, even if Devin Hester failed to return a kickoff or punt for a touchdown.